1. Field of the Invention
This invention relates to a semiconductor device and a manufacturing method thereof and more particularly to a semiconductor device having a semiconductor chip bonded on a radiator plate with interposition of a bonding layer.
2. Description of the Related Art
It has been required that consumer appliances are made compact and the requirement has called for one chip structuring of a semiconductor device or high density mounting of a semiconductor device, and thus area array packages such as ball grid array, in which external connecting terminals are arranged in the form of two-dimensional area (referred to simply as xe2x80x9cBGAxe2x80x9d hereinafter), and land grid array (referred to simply as xe2x80x9cLGAxe2x80x9d hereinafter) have been proposed and practically used to satisfy the requirement for multi-pin semiconductor.
As a related area package, tape BGA (Tape-BFA, referred to simply as xe2x80x9cT-BGAxe2x80x9d hereinafter), in which TAB (Tape Automated Bonding) is used as interconnection technique, is described referring to FIG. 2.
For example, a semiconductor chip 44 is bonded on a radiator plate 40 consisting of copper material with interposition of a paste bonding layer 42. Many electrode pads 46 are formed on the surface of the semiconductor chip 44.
On the circumference of the radiator plate 40 surrounding the semiconductor chip 44, a stiffener 50 is bonded with interposition of a bonding layer 48. On the stiffener 50, many external connecting terminals 54 having a ball-shaped end respectively are arranged dispersedly in the form of array.
These many external connecting terminals 54 are connected to the electrode pads on the semiconductor chip 44 with interposition of respective inner leads 56. These many external connecting terminals 54 are covered with an insulating film 58 excepting the ball-shaped ends and insulated stably each other. As described herein above, the external connecting terminals 54, inner leads 56, and insulating film 58 constitute a wiring pattern 60 for connecting the electrode pads of the semiconductor chip 44 to the external.
The semiconductor chip 44 bonded on the radiator plate 40 with interposition of the paste bonding layer 42 and the inner leads 56 connected to the electrode pads 46 are covered with sealing resin 62, this is so-called resin sealing.
As described herein above, in the T-BGA, because many external connecting terminals 54 are arranged dispersedly in the form of array on the stiffener 50 surrounding the semiconductor chip 44, the package size of a T-BGA is made small even if the pitch of the external connecting terminals 54 of the semiconductor device having many pins is relatively large, for example, 1.0 mm or 0.27 mm, therefore this structure is effective for high density mounting.
Further, the semiconductor chip 44 is bonded directly on the radiator plate 40 with interposition of the paste bonding layer 42, and therefore heat generated from the semiconductor element during operation is easily dissipated, thus this structure is also effective for low heat resistance packaging.
However, in the above-mentioned T-BGA, the thermal expansion coefficient of the semiconductor chip 44 is approximately 3 ppm/xc2x0 C. and the thermal expansion coefficient of the radiator plate 40 consisting of copper material is approximately 17 ppm/xc2x0 C., the large difference in the thermal expansion coefficient between both components causes the stress concentration on the paste bonding layer 42 between the semiconductor chip 44 and the radiator plate 40, for example, when the semiconductor device is subjected to a thermal cycle test (referred to simply as T/C test hereinafter), in which the temperature of the T-BGA is varied cyclically, the bonding strength of the paste bonding layer 42 is decreased to cause cracking or separation occasionally at the end.
As described herein above, though the semiconductor device is excellent in heat dissipation initially as it is fabricated, after T/C test, the bonding strength of the paste bonding layer 42 which has been subjected to stress concentration is decreased, and good contact between the semiconductor chip 44 and the radiator plate 40 is deteriorated to result in significantly reduced heat dissipation, and thus the reliability in endurance becomes poor disadvantageously.
Not only T-BGA but also semiconductors of other types as long as a bonding layer is provided between a semiconductor chip and a radiator plate or a die pad consisting of copper material are involved generally in the problem.
The present invention has been accomplished to solve the above-mentioned problem, and the object of the present invention is to provide a semiconductor device having a semiconductor chip bonded on a radiator plate with interposition of a bonding layer in which stress concentration caused in the bonding layer is relaxed to maintain the heat dissipation performance and which is excellent in reliability in endurance and a method for manufacturing thereof.
The inventors of the present invention examined the reduction of stress concentration caused in a bonding layer between bonded bodies formed of different materials due to the difference in thermal expansion coefficient between these materials to solve the above-mentioned problem.
In general, sufficiently thick thickness of a bonding layer is required to relax stress concentration on the bonding layer to be provided between a semiconductor chip and a radiator plate which have the different thermal expansion coefficient each other. However, it is difficult to form an even bonding layer having a sufficient thickness with a single layer of a related paste-based bonding layer, and a bonding layer having the sufficiently thick thickness can not be realized.
To secure an even bonding layer having a thickness sufficient for the bonding layer to relax stress concentration caused on the bonding layer, the inventors tried to use a thermoplastic film bonding layer instead of paste-based bonding layer. In this case, though it was easily achieved to form an even bonding layer having a sufficient and necessary thickness, the bonding layer was involved in the problem of blistering in at least any one of interfaces between a semiconductor chip and the thermoplastic film bonding layer or a radiator plate and the thermoplastic film bonding layer when the thermoplastic film bonding layer placed between a semiconductor chip of a hard material and a radiator plate of a hard material was press-bonded together. In detail, though no blistering was not caused when a thermoplastic film bonding layer was bonded on a semiconductor chip or a radiator plate, however, it was very difficult to prevent blistering when a radiator plate or a semiconductor chip was press-bonded on the thermoplastic film bonding layer bonded on the semiconductor chip or the radiator plate. The existence of the blister resulted in reduced bonding strength and reduced heat dissipation performance of the bonding layer.
Experiments were repeated to find a bonding layer for forming an even bonding layer having a necessary and sufficient thickness to relax stress concentration by a method in which blistering was prevented so as not to cause reduction of bonding strength and reduction of heat dissipation performance. As the result, the semiconductor device and the method for manufacturing thereof in accordance with the present invention has been accomplished.
In detail, a semiconductor device in accordance with one aspect of the present invention is a semiconductor device having a semiconductor chip bonded on a radiator plate with interposition of a bonding layer, wherein the bonding layer comprises a laminated structure including a thermoplastic film bonding layer and a paste-based bonding layer.
In the semiconductor device in accordance with one aspect of the present invention, because the laminated structure including the thermoplastic film bonding layer and the paste-based bonding layer is employed as the bonding layer for bonding the semiconductor chip on the radiator plate, an even bonding layer having a necessary and sufficient thickness is formed, and blistering, which causes reduction of bonding strength and reduction of heat dissipation of the bonding layer, is prevented.
In other words, the thermoplastic film bonding layer is served to secure the necessary and sufficient thickness of the bonding layer and to secure the evenness of the bonding layer, and on the other hand, the paste-based bonding layer formed of soft material which is provided on the one side of the thermoplastic film bonding layer is served to prevent blistering when the bonding layer is press-bonded together with the thermoplastic film bonding layer.
The semiconductor device in accordance with another aspect of the present invention is a semiconductor device described in the above-mentioned claim 1, wherein the total thickness of the thermoplastic film bonding layer and the paste-based bonding layer is in a range from 50 to 150 xcexcm, and the stress concentration suppression effect is thereby improved while the heat dissipation effect of the bonding layer having the two layer structure is maintained.
In detail, the total thickness of the thermoplastic film bonding layer and the paste-based bonding layer thinner than 50 xcexcm results in reduced stress concentration suppression effect on the bonding layer having the two layer structure though the heat dissipation effect is improved, for example, the excellent contact between the semiconductor chip and the radiator plate is deteriorated and the heat dissipation performance is decreased after T/C testing, and the reliability in endurance therefore becomes poor. On the other hand, the total thickness of the thermoplastic film bonding layer and the paste-based bonding layer thicker than 150 xcexcm results in reduced heat dissipation effect though the stress concentration suppression effect on the bonding layer having the two layer structure is improved. Accordingly, the total thickness of the thermoplastic film bonding layer and the paste-based bonding layer of 50 to 150 xcexcm is preferable to improve the stress concentration suppression effect while the heat dissipation effect of the bonding layer having the two layer structure is improved.
The thickness of the thermoplastic film bonding layer is preferably in a range form 20 to 100 xcexcm and the thickness of the paste-based bonding layer is preferably in a range from 10 to 70 xcexcm while the total thickness of the bonding layer having the two layer structure is in a range from 50 to 150 xcexcm.
The semiconductor device in accordance with another aspect of the present invention is a semiconductor described in the above-mentioned claim 1, wherein the thermoplastic film bonding layer is modified or blended with rubber-based material. For example, polyolefin-based or polyimide-based thermoplastic resin is modified or blended with silicone rubber, butadiene rubber, urethane rubber, or acrylic rubber, and the film-like thermoplastic resin bonding layer is thereby rendered soft and low in the elastic modulus, thus the larger stress concentration relaxation effect is brought about with the thinner thickness. Particularly the thermoplastic film bonding layer having the elastic modulus of 1 GPa or lower at a room temperature and the elastic modulus of 3 GPa or lower at xe2x88x9225xc2x0 C. is more effective in stress concentration suppression.
The semiconductor device in accordance with another aspect of the present invention is a semiconductor described in the above-mentioned claim 1, wherein ceramic fine powder or metal powder is mixed in the thermoplastic film bonding layer. The ceramic fine powder or metal power is served to improve the thermal conductivity of the thermoplastic film bonding layer, and thereby brings about the more improved heat dissipation performance. Examples of ceramic fine powder include, for example, fine powder of alumina, silica, and silicon nitride, and examples of metal powder include, for example, silver powder and aluminum powder.
Further, the semiconductor device in accordance with another aspect of the present invention is the above-mentioned semiconductor, wherein the paste-based bonding layer is mixed with fine powder filler. For example, the fine powder filler such as silver powder or silica powder is mixed in epoxy resin or silicone resin, and thereby improves the bonding strength and thermal conductivity of the paste-based bonding layer.
Further, the semiconductor device in accordance with another aspect of the present invention is a semiconductor device described above, wherein the paste-based bonding layer is formed of epoxy-based adhesive resin, and the epoxy-based adhesive resin is modified or blended with rubber-based material. For example, epoxy-based adhesive resin is modified or blended with silicone rubber, butadiene rubber, urethane rubber, or acrylic rubber, then the elastic modulus is thereby reduced, and such epoxy-based adhesive resin exhibits the more stress concentration relaxation effect with the thinner thickness. Particularly, the paste-based bonding layer having an elastic modulus of 1 GPa or lower at a room temperature exhibits the marked stress concentration relaxation effect.
Further, a method for manufacturing a semiconductor device in accordance with another aspect of the present invention comprises a step for coating a paste-based bonding layer on the back side of the semiconductor chip, a step for bonding a thermoplastic film bonding layer on a radiator plate, and a step for heat-press-bonding the paste-based bonding layer coated on the back side of the semiconductor chip and the thermoplastic film bonding layer bonded on the radiator plate together.
In the method for manufacturing a semiconductor device in accordance with another aspect of the present invention as described herein above, the paste-based bonding layer coated on the back side of the semiconductor chip and the thermoplastic film bonding layer bonded on the radiator plate are heat-press-bonded together to thereby form an even bonding layer having a necessary and sufficient thickness comprising the laminated structure including the thermoplastic film bonding layer and the paste-based bonding layer. In this case, blistering, which causes reduction of bonding strength and reduction of heat dissipation performance of the bonding layer, is prevented because the thermoplastic film bonding layer is bonded on the radiator plate and then the exposed side is heat-press-bonded to the paste-based bonding layer of soft material, differently from the case that the bonding layer is placed directly between the semiconductor chip and the radiator plate of hard material and press-bonded together.
A method for manufacturing a semiconductor device in accordance with another aspect of the present invention comprises a step for bonding a thermoplastic film bonding layer on a radiator plate, a step for coating a paste-based bonding layer on the thermoplastic film bonding layer, and a step for press-bonding the semiconductor chip on the paste-based bonding layer.
In the method for manufacturing a semiconductor in accordance with another aspect of the present invention, as described herein above, the paste-based bonding layer is bonded on the thermoplastic film bonding layer bonded on the radiator plate to thereby form an even bonding layer having a necessary and sufficient thickness comprising the laminated structure including the thermoplastic film bonding layer and the paste-based bonding layer. Because the paste bonding layer of soft material is coated on the exposed surface of the thermoplastic film bonding layer after the thermoplastic film bonding layer has been bonded on the radiator plate, blistering, which causes reduction of bonding strength and reduction of heat dissipation performance of the bonding layer, is prevented, diffidently from the case that the bonding layer is placed directly between the semiconductor chip and the radiator plate of hard material and then press-bonded together.